This invention relates to synthetic polymer filaments of rectangular cross-section which have been textured in such a manner as to render them essentially non-directional and suitable for use in synthetic turf products, such as golf greens.
A considerable commercial interest has developed in synthetic or man-made turfs. Fur example, the product disclosed in U.S. Pat. No. 3,328,828 consists of filaments which are tufted into a backing. To resemble natural turf, the filaments must be of heavy denier (e.g., 100 or above). However, with such large filaments, flexibility becomes a problem which is overcome by the use of filaments with a rectangular cross-section (width/thickness &gt;3/1). However, rectangulr filaments have a tendency to bend only along the longitudinal axis and this tendency increases as the size of the filament increases. i.e., the rectangular filaments are said to have a directional character. After tufting, weaving, or knitting to form turf, the flat rectangular, ribbon-like filaments are oriented uniformly with the result that the pile lays preferentially in the direction corresponding with the directional tendency of the filaments. It can be seen intuitively that in stroking an object across the pile surface, such as a golf ball, if the ball is stroked with the pile lay, the surface will roll much faster than if the ball is stroked against the pile lay. A ball stroked at an angle to the pile lay will tend to deviate from its natural course.
To overcome the directional drawbacks of large rectangulr filaments, it has been suggested (e.g., see U.S. Pat. No. 3,565,742) that short lengths of filaments be flocked onto an adhesive-covered backing to achieve a more random orientation of the filaments. This procedure, however, cannot be performed on conventional tufting, knitting, or weaving machinery. Many other techniques have also been tried to minimize the directional tendencies of the synthetic turf surface. See, for example, U.S. Pat. Nos. 3,513,061 and 3,513,062.
Another problem associated with large rectangular filaments, in addition to their tendency to bend only along the longitudinal axis, is the low covering power of such filaments. To overcome this problem in artificial turf, U.S. Pat. No. 3,681,912 suggests texturing the filaments by twisting the filaments and passing the filament edges over a heated surface. Intuitively, it can be seen that this process imparts a relatively small and uniform amount of texturing to the filaments, i.e., it is questionable how much the natural stiffness and directional tendencies of the filaments are reduced. Additionally, such processes are generally not suitable to high speed performance.